containerd is an industry-standard container runtime with an emphasis on simplicity, robustness and portability. It is available as a daemon for Linux and Windows, which can manage the complete container lifecycle of its host system: image transfer and storage, container execution and supervision, low-level storage and network attachments, etc..
There is a [v0.2.x](https://github.com/docker/containerd/tree/v0.2.x) branch for the current release of containerd that is being consumed by Docker and others and the master branch is the development branch for the 1.0 roadmap and feature set.
Any PR or issue that is intended for the current v0.2.x release should be tagged with the same `v0.2.x` tag.
### Communication
For async communication and long running discussions please use issues and pull requests on the github repo.
This will be the best place to discuss design and implementation.
For sync communication we have a community slack with a #containerd channel that everyone is welcome to join and chat about development.
To build the daemon and `ctr` simple test client, the following build system dependencies are required:
* Go 1.7.x or above
* Protoc 3.x compiler and headers (download at the [Google protobuf releases page](https://github.com/google/protobuf/releases)
For proper results, install the `protoc` release into `/usr/local` on your build system. For example, the following commands will download and install the 3.1.0 release for a 64-bit Linux host:
With the required dependencies installed, the `Makefile` target named **binaries** will compile the `ctr` and `containerd` binaries and place them in the `bin/` directory. Using `sudo make install` will place the binaries in `/usr/local/bin`. When making any changes to the gRPC API, `make generate` will use the installed `protoc` compiler to regenerate the API generated code packages.
Vendoring of external imports uses the [`vndr` tool](https://github.com/LK4D4/vndr) which uses a simple config file, `vendor.conf`, to provide the URL and version or hash details for each vendored import. After modifying `vendor.conf` run the `vndr` tool to update the `vendor/` directory contents. Combining the `vendor.conf` update with the changeset in `vendor/` after running `vndr` should become a single commit for a PR which relies on vendored updates.
Containerd will by default use `runc` found via the $PATH as the OCI-compliant runtime. You can specify the runtime directly with the `runtime` flag when starting containerd. However you specify the runtime, the expectation is that during the pre-release development cycle for containerd, the supported version of `runc` will track the current master branch of [`opencontainers/runc`](https://github.com/opencontainers/runc).
The APIs for images and containers should be designed in a way that when used together the components have a natural flow but still be useful independently.
The execution layer and overlay filesystems can be used independently but if you were to use both, they share a common `Mount` struct that the filesystems produce and the execution layer consumes.
Breaking up the filesystem APIs to allow snapshots, copy functionality, and mounts allow people implementing build at the higher levels more flexibility.
For the various components in containerd there should be defined extension points where implementations can be swapped for alternatives.
The best example of this is that containerd will use `runc` from OCI as the default runtime in the execution layer but other runtimes conforming to the OCI Runtime specification they can be easily added to containerd.
Additional implementations will not be accepted into the core repository and should be developed in a separate repository not maintained by the containerd maintainers.
containerd will be released with a 1.0 when feature complete and this version will be supported for 1 year with security and bug fixes applied and released.
Minor (0.x.0) version will always be compatible with the previous minor release. i.e. 1.2.0 is backwards compatible with 1.1.0 and 1.1.0 is compatible with 1.0.0.
| distribution | Having the ability to push and pull images as well as operations on images as a first class API object | in | containerd will fully support the management and retrieval of images |
| build | Building images as a first class API | out | Build is a higher level tooling feature and can be implemented in many different ways on top of containerd |
| volumes | Volume management for external data | out | The API supports mounts, binds, etc where all volumes type systems can be built on top of containerd. |
| logging | Persisting container logs | out | Logging can be build on top of containerd because the container’s STDIO will be provided to the clients and they can persist any way they see fit. There is no io copying of container STDIO in containerd. |
containerd is designed to be embedded into a larger system, hence it only includes a barebone CLI (`ctr`) specifically for development and debugging purpose, with no mandate to be human-friendly, and no guarantee of interface stability over time.
containerd should provide the primitives to create, add, remove, or manage network interfaces and network namespaces for a container but IP allocation, discovery, and DNS should be handled at higher layers.
